Piezoelectric nanocomposite sensors assembled using zinc oxide nanoparticles and poly(vinylidene fluoride)

John S. Dodds,Kenneth J. Loh,Frederick N. Meyers 국제구조공학회 2013 Smart Structures and Systems, An International Jou Vol.12 No.1

Structural health monitoring (SHM) is vital for detecting the onset of damage and for preventing catastrophic failure of civil infrastructure systems. In particular, piezoelectric transducers have the ability to excite and actively interrogate structures (e.g., using surface waves) while measuring their response for sensing and damage detection. In fact, piezoelectric transducers such as lead zirconate titanate (PZT) and poly(vinylidene fluoride) (PVDF) have been used for various laboratory/field tests and possess significant advantages as compared to visual inspection and vibration-based methods, to name a few. However, PZTs are inherently brittle, and PVDF films do not possess high piezoelectricity, thereby limiting each of these devices to certain specific applications. The objective of this study is to design, characterize, and validate piezoelectric nanocomposites consisting of zinc oxide (ZnO) nanoparticles assembled in a PVDF copolymer matrix for sensing and SHM applications. These films provide greater mechanical flexibility as compared to PZTs, yet possess enhanced piezoelectricity as compared to pristine PVDF copolymers. This study started with spin coating dispersed ZnO- and PVDF-TrFE-based solutions to fabricate the piezoelectric nanocomposites. The concentration of ZnO nanoparticles was varied from 0 to 20 wt.% (in 5 % increments) to determine their influence on bulk film piezoelectricity. Second, their electric polarization responses were obtained for quantifying thin film remnant polarization, which is directly correlated to piezoelectricity. Based on these results, the films were poled (at 50 MV-m-1) to permanently align their electrical domains and to enhance their bulk film piezoelectricity. Then, a series of hammer impact tests were conducted, and the voltage generated by poled ZnO-based thin films was compared to commercially poled PVDF copolymer thin films. The hammer impact tests showed comparable results between the prototype and commercial samples, and increasing ZnO content provided enhanced piezoelectric performance. Lastly, the films were further validated for sensing using different energy levels of hammer impact, different distances between the impact locations and the film electrodes, and cantilever free vibration testing for dynamic strain sensing.

Piezoelectric nanocomposite sensors assembled using zinc oxide nanoparticles and poly(vinylidene fluoride)

Dodds, John S.,Meyers, Frederick N.,Loh, Kenneth J. Techno-Press 2013 Smart Structures and Systems, An International Jou Vol.12 No.1

Structural health monitoring (SHM) is vital for detecting the onset of damage and for preventing catastrophic failure of civil infrastructure systems. In particular, piezoelectric transducers have the ability to excite and actively interrogate structures (e.g., using surface waves) while measuring their response for sensing and damage detection. In fact, piezoelectric transducers such as lead zirconate titanate (PZT) and poly(vinylidene fluoride) (PVDF) have been used for various laboratory/field tests and possess significant advantages as compared to visual inspection and vibration-based methods, to name a few. However, PZTs are inherently brittle, and PVDF films do not possess high piezoelectricity, thereby limiting each of these devices to certain specific applications. The objective of this study is to design, characterize, and validate piezoelectric nanocomposites consisting of zinc oxide (ZnO) nanoparticles assembled in a PVDF copolymer matrix for sensing and SHM applications. These films provide greater mechanical flexibility as compared to PZTs, yet possess enhanced piezoelectricity as compared to pristine PVDF copolymers. This study started with spin coating dispersed ZnO- and PVDF-TrFE-based solutions to fabricate the piezoelectric nanocomposites. The concentration of ZnO nanoparticles was varied from 0 to 20 wt.% (in 5 % increments) to determine their influence on bulk film piezoelectricity. Second, their electric polarization responses were obtained for quantifying thin film remnant polarization, which is directly correlated to piezoelectricity. Based on these results, the films were poled (at 50 $MV-m^{-1}$) to permanently align their electrical domains and to enhance their bulk film piezoelectricity. Then, a series of hammer impact tests were conducted, and the voltage generated by poled ZnO-based thin films was compared to commercially poled PVDF copolymer thin films. The hammer impact tests showed comparable results between the prototype and commercial samples, and increasing ZnO content provided enhanced piezoelectric performance. Lastly, the films were further validated for sensing using different energy levels of hammer impact, different distances between the impact locations and the film electrodes, and cantilever free vibration testing for dynamic strain sensing.

Analysis of the Energy Efficiency and Clothing Comfort of Garment Design on Piezoelectricity Harvest

양진희,조현승,이주현 한국감성과학회 2020 춘계학술대회 Vol.2020 No.-

In our previous study, we evaluated the efficiency of piezoelectricity during joint movement according to the tightness level (4 levels) and garment design (3 types). As a result, the harvested piezoelectricity increased with increasing levels of tightness level and the efficiency of the design that maximizes the curvature of piezoelectricity harvester was high. Clothing for energy harvesting is not only its performance, but also the clothing comfort level is very important. Therefore, the subjective clothing comfort level was evaluated on the basis of the three parameters (pressure sensation level, activity sensation level, and thermal sensation level). The comfort level of the clothing was derived on the basis of the tightness level of the seamless knit, design structure of the garment, area of energy harvesting, and frequency of motion; further, the comfort level was calculated on the basis of the arithmetic mean of the three parameters. Thus, it was found that a garment that was seamless knit by taking into account the T3(tightness level) and D3(reinforced 3D design) was not only effective in the harvesting of piezoelectricity but it was also comfortable to wear. Sportswear for physical sports such as cycling, climbing, rowing, and cross-fit were designed on the basis of the requirements of garment design established in this study; further, the results of this study prove that it is possible to design a garment that can not only be used as sportswear but can also be used for the harvesting of piezoelectricity.

Atomic-scale symmetry breaking for out-of-plane piezoelectricity in two-dimensional transition metal dichalcogenides

Kang, Seunghun,Kim, Sera,Jeon, Sera,Jang, Woo-Sung,Seol, Daehee,Kim, Young-Min,Lee, Jaekwang,Yang, Heejun,Kim, Yunseok Elsevier 2019 Nano energy Vol.58 No.-

<P><B>Abstract</B></P> <P>It is known that only in-plane piezoelectricity exists in pristine two dimensional (2D) transition metal dichalcogenides (TMDs). In this study, we demonstrate the creation of strong out-of-plane piezoelectricity in semiconducting 2H-MoTe<SUB>2</SUB> flakes by an artificial atomic-scale symmetry breaking. The atomic-scale symmetry breaking associated with flexoelectricity was realized through Te vacancy formation by a simple thermal annealing of the 2D TMDs. The strong out-of-plane piezoelectricity was experimentally measured and confirmed by theoretical calculations. This strategy of atomic-scale symmetry modulation for out-of-plane piezoelectricity can be easily applied to a broader class of 2D TMD materials that have not been used for applications with out-of-plane piezoelectricity. Accordingly, it can stimulate the expansion of practical energy device applications with 2D TMD materials.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Achievement of strong out-of-plane piezoelectricity. </LI> <LI> Atomic-scale symmetry breaking via Te vacancy formation. </LI> <LI> Simple strategy for inducing out-of-plane piezoelectricity by thermal annealing. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Tunable Out-of-Plane Piezoelectricity in Thin-Layered MoTe₂ by Surface Corrugation-Mediated Flexoelectricity

Kang, Seunghun,Jeon, Sera,Kim, Sera,Seol, Daehee,Yang, Heejun,Lee, Jaekwang,Kim, Yunseok American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.32

<P>Piezoelectricity crystallographically exists only in the in-plane direction in two-dimensional transition metal dichalcogenides. Here, we demonstrated flexoelectricity-tunable out-of-plane piezoelectricity in semiconducting 2H-MoTe<SUB>2</SUB> flakes by creating surface corrugation. In particular, the strong out-of-plane piezoelectricity and its spatial variation depending on local flexoelectricity was observed even though crystallographically there exists only in-plane piezoelectricity. Surface corrugation-mediated flexoelectricity tuning can be applied to other two-dimensional or thin-layered materials and, furthermore, the results could provide useful information on the interweaving nature between mechanical stimulus and electric dipole in low-dimensional materials.</P> [FIG OMISSION]</BR>

A Lead-free Flexible Structure for Piezoelectric Power Generation

Byung Woo Kho,윤병길,정종훈,이민백 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.12

Here, we demonstrate a fully-flexible piezoelectric hybrid structure composed of sodium niobatenanocubes and polyvinylidene fluoride. Hydrothermally-grown sodium niobate nanocubes show anorthorhombic crystal structure with Pmc21 symmetry, and polyvinylidene fluoride is electricallypoled for the -phase, each of those represents piezoelectricity. Hybrid devices were electricallytested in two different modes by applying forces parallel to the in-plane and the out-of-plane directionsof the piezoelectric layer. Our device shows an output voltage, current, and power density of2.9 V, 68 nA, and 4.4 μWcm−3, respectively, at a pushing force of 5 kgf and a frequency of 1 Hz. The output power generation also shows a linear relation with the applied force over a wide range of1 − 5 kgf. This implies our flexible hybrid piezoelectric structure can be adapted to various mechanicalenvironments. Our unique structure should open up various application areas of piezoelectricmaterials such as touch sensors, flexible energy harvesters and eco-friendly piezoelectric actuators.

Poly(vinylidene fluoride) 다층 필름의 제조 및 특성

손태원(Tae Won Son),김종환(Jong Hwan Kim),최원미(Won Mi Choi),한비비(Fei Fei Han),권오경(Oh Kyeong Kwon) 한국고분자학회 2011 폴리머 Vol.35 No.2

전자 기기의 빠른 발전에 따른 무선 기기들의 사용은 급격히 늘어나고 있다. 그래서 이런 제품에 자가 발전이 가능한 재료를 적용시키는 사례가 점차 늘고 있다. 여기에 사용되는 재료로서 poly(vinylidene fluoride)(PVDF)가 있는데 PVDF는 piezoelectricity를 낼 수 있는 특별한 결정구조인 β-phase를 가지고 있다. 이 논문에서는 piezoelectricity에 결정적인 영향인 β-phase 함량을 증가시키기 위해 다층 PVDF 필름을 제조하였다. 이 PVDF 필름은 용매인 DMAc에 10%로 용해시킨 것으로 spin rate는 850 rpm, spin time은 60초이며 건조온도는 60 ℃이다. 비교적으로 다층 필름은 단일 층보다 더 높은 β-phase함량을 나타내었다. 이 β-phase함량은 4-layer 필름이 되기까지 점차 증가되었으며 최대 함량은 7.72이다. Along with the fast development of electronics, the demands of portable electronics and wireless sensors are growing rapidly. The need for self-powering materials capable of powering the electrical devices attached to them is increasing. The piezoelectric effect of polyvinylidene fluoride (PVDF) can be used for this purpose. PVDF has a special crystal structure consisting of a β-phase that can produce piezoelectricity. In this paper, multilayer PVDF films were fabricated to increase the β-phase content. A solution of 10% concentration N,N-dimethylacetamide (DMAc) in PVDF (PVDF/DMAc) was used to fabricate the films via spin coating technique with the following optimum process parameters: a spin rate of 850 rpm, spin time of 60 s, drying temperature of 60 ℃, and drying time of 30 min. Compared with single-layer PVDF films, the multilayer films exhibited higher β-phase content. The β-phase content of the films increased gradually with increasing number of layers until 4. Maximum ratio of β-phase content was 7.72.

New insights in piezoelectric free-vibrations using simplified modeling and analyses

Benjeddou, Ayech Techno-Press 2009 Smart Structures and Systems, An International Jou Vol.5 No.6

New insights are presented in simplified modeling and analysis of free vibrations of piezoelectric - based smart structures and systems. These consist, first, in extending the wide used piezoelectric-thermal analogy (TA) simplified modeling approach in currently static actuation to piezoelectric free-vibrations under short-circuit (SC) and approximate open-circuit (OC) electric conditions; second, the popular piezoelectric strain induced - potential (IP) simplified modeling concept is revisited. It is shown that the IP resulting frequencies are insensitive to the electric SC/OC conditions; in particular, SC frequencies are found to be the same as those resulting from the newly proposed OC TA. Two-dimensional plane strain (PStrain) and plane stress (PStress) free-vibrations problems are then analyzed for above used SC and approximate OC electric conditions. It is shown theoretically and validated numerically that, for both SC and OC electric conditions, PStress frequencies are lower than PStrain ones, and that 3D frequencies are bounded from below by the former and from above by the latter. The same holds for the modal electro-mechanical coupling coefficient that is retained as a comparator of presented models and analyses.

New insights in piezoelectric free-vibrations using simplified modeling and analyses

Ayech Benjeddou 국제구조공학회 2009 Smart Structures and Systems, An International Jou Vol.5 No.6

New insights are presented in simplified modeling and analysis of free vibrations of piezoelectric-based smart structures and systems. These consist, first, in extending the wide used piezoelectric–thermal analogy (TA) simplified modeling approach in currently static actuation to piezoelectric free–vibrations under short-circuit(SC) and approximate open-circuit (OC) electric conditions; second, the popular piezoelectric strain induced –potential (IP) simplified modeling concept is revisited. It is shown that the IP resulting frequencies are insensitive to the electric SC/OC conditions; in particular, SC frequencies are found to be the same as those resulting from the newly proposed OC TA. Two-dimensional plane strain (PStrain) and plane stress (PStress) free-vibrations problems are then analyzed for above used SC and approximate OC electric conditions. It is shown theoretically and validated numerically that, for both SC and OC electric conditions, PStress frequencies are lower than PStrain ones, and that 3D frequencies are bounded from below by the former and from above by the latter. The same holds for the modal electro-mechanical coupling coefficient that is retained as a comparator of presented models and analyses.

Controlled conductivity of p-type Cu_xO/GaN piezoelectric generator to harvest very high piezoelectric potential

Johar, Muhammad Ali,Kang, Jin-Ho,Ha, Jun-Seok,Lee, June Key,Ryu, Sang-Wan ELSEVIER SCIENCE 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.726 No.-

<P><B>Abstract</B></P> <P>Typically, semiconductor piezoelectric-generators (PGs) exhibit low output potential because of the rapid screening by mobile carriers, and the output potential drops within fractions of a second. The reduction of internal carrier screening has been attempted by several groups, but complete suppression has not yet been reported. In this paper, a novel method for the fabrication of high-power PGs is presented. The detrimental screening issue was solved by fabricating a p–n heterojunction of p-type Cu<SUB>x</SUB>O (x = 1, 2) and GaN. This was found to be an effective structure for decreasing the internal screening, while the suppression of screening was directly proportional to the resistivity of the p-type layer. The resistivity of the p-type thin film was controlled by optimizing the oxygen content in the environment during deposition. From X-ray diffraction analysis, the crystal structure of copper oxide changed by varying the oxygen incorporation, which primarily controlled the p-type conductivity. The optimized device exhibited output voltage of 26 V with a current density of 11.40 μA cm<SUP>−2</SUP> under a pressure of 5 MPa. This study provides an effective approach for generating high electrical power, and it would be advantageous to construct flexible GaN PGs, which are essential devices for self-powered sensor networks.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Controlled conductivity of p-type Cu<SUB>x</SUB>O for Cu<SUB>x</SUB>O/GaN PG was fabricated. </LI> <LI> Junction screening was addressed to enhance piezoelectric output. </LI> <LI> Piezoelectric output of PG was 26 V and 11.4 μA cm<SUP>−2</SUP> with an efficiency of 2.6%. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>